Data transmission lines are installed in their millions nowadays, for example for the purpose of supplying private households or companies with comparatively broadband data connections. By way of example, currently approximately 20 million DSL connections (Digital Subscriber Line connections), in particular ADSL connections (Asymmetric Digital Subscriber Line connections) or VDSL connections (Very High Bitrate Digital Subscriber Line connections), are currently set up in the copper conductor pair network of Deutsche Telekom AG in Germany. Depending on the operating state and configuration of these systems, the power spectral densities (so-called PSD spectra, Power Spectral Density spectra) that can be measured on individual data transmission lines of such data transmission systems can deviate considerably from the power spectral density striven for.
Hitherto, the measurement of individual data transmission lines of such data transmission systems has been able to be realized only with various disadvantages being accepted. Said disadvantages include, inter alia, comparatively low measurement accuracy particularly when measuring the power spectral density, and often the necessity that, for carrying out the measurement of a predefined data transmission line, the latter has to be isolated, i.e. interrupted.